Rookie Malik Willis has taken 18 regular-season snaps as an NFL quarterback. On Sunday, he could be in for a whole lot more.

Ryan Tannehill has started the past 55 regular-season and playoff games at quarterback for the Tennessee Titans. But Tannehill sustained an ankle injury in Sunday’s 19-10 victory over the Indianapolis Colts.

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The Titans’ injury and participation report indicates Tannehill did not practice on Wednesday and Friday and was a limited participant on Thursday. His chances of playing on Sunday against the Houston Texans are listed as questionable.

Tennessee is holding out hope that Tannehill can play in Sunday’s game.

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“We’re going to try to give it as much time as we possibly can,” Titans coach Mike Vrabel said on Friday. “We feel like we’re prepared with whatever may happen. We’ll see how it goes. We still have some time before the game.”

Willis is on standby to step in if Tannehill can’t play.

Willis said he and Tennessee’s practice-squad quarterback, Logan Woodside, had tried not to alter their routines.

“We got to prepare like we’re going to be the starter every week,” Willis said, “not just when we got a guy banged up and we don’t know what’s going to go down. Like I said, me and Logan try to prepare like we are starters every week regardless of what the situation might be.”

But with Tannehill out of practice, Willis got much more work with the Titans’ first-team offense this week.

“I thought he took advantage of his opportunities,” Vrabel said. “Tried to lead and function as our quarterback.”

Willis said Tannehill had been helping prep him in case the No. 1 QB can’t go on Sunday.

“He’s been really cool,” Willis said. “He’s always been able to answer questions if I had them. He’s just being a good guy out there and helping us out, telling us what he thinks. And that’s what it’s about. It’s about how we’re thinking out there more than anything – decision-making and whatnot.”

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As Jarrett Stidham’s backup at Auburn, Willis completed 11-of-14 passes for 69 yards with one touchdown and no interceptions and ran for 309 yards and two touchdowns on 28 carries in 2017 and 2018 with the Tigers. After transferring to Liberty, Willis completed 377-of-604 passes for 5,107 yards with 47 touchdowns and 18 interceptions and ran for 1,822 yards and 27 touchdowns on 338 carries in two seasons with the Flames.

The Titans took Willis with a third-round choice in the NFL Draft on April 29.

With Tannehill sitting out, Willis started Tennessee’s three preseason games. In addition to completing 28-of-51 passes for 318 yards with two touchdowns and one interception, Willis led the AFC with 159 yards and one touchdown on 14 rushing attempts. He had the conference’s longest preseason run at 50 yards.

Willis made his NFL debut in the Titans’ second game, when he completed 1-of-4 passes for 6 yards and ran four times for 16 yards mopping up in the Titans’ 41-7 loss to the Buffalo Bills on Sept. 19.

Willis didn’t take another snap until Sunday.

Willis handed off to running back Dontrell Hilliard after Tannehill limped off the field, then the Tennessee field-goal unit came in for a three-pointer that gave the Titans a 16-7 lead with 13:47 left to play.

When Tennessee regained possession of the football, Tannehill returned and competed the game.

The Titans take a four-game winning streak to Houston, where they play the Texans at 3:05 p.m. CDT Sunday at NRG Stadium.

“I’m blessed,” Willis said. “I’m just going to go out there and have fun and see where the chips fall.”

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Mark Inabinett is a sports reporter for Alabama Media Group. Follow him on Twitter at @AMarkG1.